Digital Movie Gallery

These digital movies illustrate some of the concepts discussed in Astronomy
162. With slight modification, they are identical to the movies being
shown in lecture. Since these movies are experimental, your feedback would be greatly
appreciated.

Most of the movies are available in one or more of the following three
formats: QuickTime, MPEG, and animated GIF. QT viewers are readily
available as plug-in options for common PC and Mac browsers (e.g., Netscape
and Internet Explorer). MPEG is the de facto standard in the Unix world
(although Unix users should note that the latest versions of "xanim"
support QT movies). Animated GIFs may be viewed using most browsers, and
with the xanim tool on Unix boxes. In most cases, the animated GIF
versions are reduced in size and length to facilitate easy downloads for
slow connections.

This movie demonstrates Trigonometic Parallax. The top half of each frame
shows the appearance of the sky as seen from the Earth (ignoring the Sun),
and the bottom half shows a fixed view looking down from above onto the
plane of the Earth's orbit around the Sun (the ecliptic). A red star is
shown located some distance to the right (also in the ecliptic plane). In
this simulation, the star is fixed in space with respect to the Sun, and
its proximity to the Sun is greatly exaggerated to help make its parallax
easy to see.

In the first half of the movie, the parallax motion of the red star over
the course of one year is shown. Note that the star is not moving through
space, as can be seen in the bottom panel, only the Earth is
moving. The star's parallax motion is simply a reflection of the Earth's
orbital motion. When viewed from the moving Earth (top panel), the red
star appears to move first west (towards the right) then east (towards the
left) with respect to the distant background stars which are so far away
that their parallax motions are too small to be seen at this
scale.

In the second half, we move the star 2x farther away (as indicated by the
scale bar at the bottom) and run through another year. Now the annual the
trigonometric parallax motions are 2x smaller because the distance
to the star is 2x greater. This fact, that the trigonometric
parallax of a star is inversely proportional to its distance from the Sun
gives us a direct measurement of the star's distance.

Note that the parallax motion of the star is an illusion due to the
orbital motion of the Earth around the Sun. Real stars are much more
distant than shown here. For example, one of the nearest stars, Alpha
Centauri, is about 277,000 AU away, resulting in a parallax of about
0.74 arcseconds.

This movie shows the appearance of the Big Dipper (Ursa Major) for a
200,000 year period between 100,000 BC and 100,000 AD demonstrating the
proper motion of the stars. All stars down to 6.5 magnitude are shown, and
the timestep is 1000 years. Most of the bright stars making up the
familiar constellation of the Big Dipper are part of a moving group, and
can clearly be seen to be moving together towards the East (left on the
frame) over time. Watch for very fast moving stars that cross the field
over the 200,000 year period of this animation.

Circular Orbit:

Elliptical Orbit (e=0.4):

These movies simulate the orbit of a visual binary star pair consisting of
an F0v primary and M0v secondary. The orbital plane of the two is in the
plane of the sky. The two stars have a mass ratio of about 3.6,
appropriate for stars of this type.

The first movie shows the two stars in circular orbits about their center
of mass (marked with the green dot). Two orbits are shown, with the orbit
traced as a white line. Both stars move at a uniform speed around the
center of mass, the more massive, blueish F0v star moves less as it is
closer to the center-of-mass than the less massive, reddish M0v star.

The second movie shows the two stars in elliptical orbits about their
center of mass, with an orbital eccentricity of 0.4. Watch how both stars
noticeably speed up and slow down as they pass periastron (closest approach
to the C-of-M) and apastron (farthest from C-of-M), respectively, thus
obeying Kepler's Second Law (equal areas in equal times) the same as the
planets in the Solar System.

This movie simulates a double-lined spectroscopic binary star system
consisting of an F0v primary and M0v secondary in a circular orbit about
each other. The orbital plane is oriented along the line of sight in this
simulation. The top half of the frame shows the appearance of the two
stars seen from above, with the red dot marking the center of mass of the
system, and the green dot at left indicating the location of the distant
observer. The bottom half of the frame shows the spectrum seen by the
distant observer. The absorption lines from the primary star are labeled
"A", while those from the secondary star are labeled "B". As the two stars
orbit each other, they alternately move towards then away from the
observer. This results in their absorption-line spectra getting
blue-shifted, then red-shifted, respectively. The pattern of Doppler
shifts traces out the orbital motions of each star. A thin "stationary"
absorption line appearing between the two lines shows the un-shifted
location of each line.

Notice that the primary star's absorption lines (labeled "A") only shift a
small amount, reflecting its smaller orbital velocity, compared to that of
the secondary, which moves much faster. This because the lower mass
secondary star must be located farther from the center-of-mass of the
system than the primary, and so has to trace out a much bigger circle in
its orbit in the same time that the primary does, making its Doppler shift
larger in proportion to their mass ratio.

The amount of Doppler shift seen in this simulation has been greatly
exaggerated to make it easily visible.

This movie simulates an eclipsing binary star system consisting of an A0v
primary and G5v secondary in a circular orbit about each other. The
orbital plane is tilted with respect to the line of sight by 6°. The
top half of the frame shows the appearance of the two stars, with the red
dot marking the center of mass of the system (just outside the radius of
the blueish A0v primary star). The light curve of the total system is
traced out in the lower panel as they orbit. Two orbits full orbits are
shown, with a red marker used on the light curve to show the current
location.

Notice that the deepest eclipse occurs when the secondary is in front of
the primary. This is because of the nearly factor of two greater effective
temperature of the primary (10,000K compared to 5,500K). Since surface
brightness scales like T4, more light is blocked when the
secondary is blocking part of the primary, than when the primary completely
blocks the secondary.